Evaluating effects of partial fishing closures on the composition and structure of estuarine fish assemblages

Partial fishing closures are an integral component of contemporary aquatic resource conservation and fisheries management. This study examined whether assemblages of fishes differed between partially closed (PC) estuaries that permit recreational fishing compared to fully fished (FF) estuaries that permit commercial and recreational fisheries. Fish assemblages were quantitatively sampled in a standard and stratified manner using a multimesh gillnet and beam trawl that sampled different ichthyofaunal components in two PC and two FF estuaries across three years, ∼ six to eight years post commercial fishing closure and PC implementation. There was no global support for the hypothesis that assemblages, diversity and numbers of fishes would differ between PC and FF estuaries. Assemblages significantly and consistently differed among individual estuaries regardless of estuary management category. Differences between PC and FF estuaries in terms of numbers of species and individuals were inconsistent across years, with more species (gillnet) and individuals (trawl) occurring in PC estuaries in only one of three years. Only one species (Gerres subfasciatus) was more abundant (gillnet) in the PC category, most likely due to reduced fishery harvests. In contrast, juveniles of three harvested species (G. subfasciatus, Rhabdosargus sarba and Acanthopagrus spp.) occurred in greater numbers (trawl) in FF estuaries, potentially a result of strong recruitment and estuary-specific environmental conditions. This study demonstrated the complexity, and potential scale-dependent ecological and fishery-related constraints, in comparatively examining the effects of different fishery management arrangements on fish assemblages across estuary systems.